upstream commit

Host key rotation support.

Add a hostkeys@openssh.com protocol extension (global request) for
a server to inform a client of all its available host key after
authentication has completed. The client may record the keys in
known_hosts, allowing it to upgrade to better host key algorithms
and a server to gracefully rotate its keys.

The client side of this is controlled by a UpdateHostkeys config
option (default on).

ok markus@

1 files changed, 190 insertions, 16 deletions

diff --git a/hostfile.c b/hostfile.c
index ccb2af920..9de1b383b 100644
--- a/hostfile.c
+++ b/hostfile.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: hostfile.c,v 1.61 2015/01/18 21:48:09 djm Exp $ */
+/* $OpenBSD: hostfile.c,v 1.62 2015/01/26 03:04:45 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -39,6 +39,7 @@
 #include "includes.h"
 
 #include <sys/types.h>
+#include <sys/stat.h>
 
 #include <netinet/in.h>
 
@@ -49,6 +50,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <stdarg.h>
+#include <unistd.h>
 
 #include "xmalloc.h"
 #include "match.h"
@@ -430,6 +432,29 @@ lookup_key_in_hostkeys_by_type(struct hostkeys *hostkeys, int keytype,
             found) == HOST_FOUND);
 }
 
+static int
+write_host_entry(FILE *f, const char *host,
+    const struct sshkey *key, int store_hash)
+{
+        int r, success = 0;
+        char *hashed_host = NULL;
+
+        if (store_hash) {
+                if ((hashed_host = host_hash(host, NULL, 0)) == NULL) {
+                        error("%s: host_hash failed", __func__);
+                        return 0;
+                }
+        }
+        fprintf(f, "%s ", store_hash ? hashed_host : host);
+
+        if ((r = sshkey_write(key, f)) == 0)
+                success = 1;
+        else
+                error("%s: sshkey_write failed: %s", __func__, ssh_err(r));
+        fputc('\n', f);
+        return success;
+}
+
 /*
  * Appends an entry to the host file.  Returns false if the entry could not
  * be appended.
@@ -439,32 +464,181 @@ add_host_to_hostfile(const char *filename, const char *host,
     const struct sshkey *key, int store_hash)
 {
         FILE *f;
-        int r, success = 0;
-        char *hashed_host = NULL;
+        int success;
 
         if (key == NULL)
                 return 1;       /* XXX ? */
         f = fopen(filename, "a");
         if (!f)
                 return 0;
+        success = write_host_entry(f, host, key, store_hash);
+        fclose(f);
+        return success;
+}
 
-        if (store_hash) {
-                if ((hashed_host = host_hash(host, NULL, 0)) == NULL) {
-                        error("%s: host_hash failed", __func__);
-                        fclose(f);
+struct host_delete_ctx {
+        FILE *out;
+        int quiet;
+        const char *host;
+        int *skip_keys;
+        struct sshkey * const *keys;
+        size_t nkeys;
+};
+
+static int
+host_delete(struct hostkey_foreach_line *l, void *_ctx)
+{
+        struct host_delete_ctx *ctx = (struct host_delete_ctx *)_ctx;
+        int loglevel = ctx->quiet ? SYSLOG_LEVEL_DEBUG1 : SYSLOG_LEVEL_INFO;
+        size_t i;
+
+        if (l->status == HKF_STATUS_HOST_MATCHED) {
+                if (l->marker != MRK_NONE) {
+                        /* Don't remove CA and revocation lines */
+                        fprintf(ctx->out, "%s\n", l->line);
+                        return 0;
+                }
+
+                /* XXX might need a knob for this later */
+                /* Don't remove RSA1 keys */
+                if (l->key->type == KEY_RSA1) {
+                        fprintf(ctx->out, "%s\n", l->line);
                         return 0;
                 }
+
+                /*
+                 * If this line contains one of the keys that we will be
+                 * adding later, then don't change it and mark the key for
+                 * skipping.
+                 */
+                for (i = 0; i < ctx->nkeys; i++) {
+                        if (sshkey_equal(ctx->keys[i], l->key)) {
+                                ctx->skip_keys[i] = 1;
+                                fprintf(ctx->out, "%s\n", l->line);
+                                debug3("%s: %s key already at %s:%ld", __func__,
+                                    sshkey_type(l->key), l->path, l->linenum);
+                                return 0;
+                        }
+                }
+
+                /*
+                 * Hostname matches and has no CA/revoke marker, delete it
+                 * by *not* writing the line to ctx->out.
+                 */
+                do_log2(loglevel, "%s%s%s:%ld: Host %s removed",
+                    ctx->quiet ? __func__ : "", ctx->quiet ? ": " : "",
+                    l->path, l->linenum, ctx->host);
+                return 0;
         }
-        fprintf(f, "%s ", store_hash ? hashed_host : host);
+        /* Retain non-matching hosts and invalid lines when deleting */
+        if (l->status == HKF_STATUS_INVALID) {
+                do_log2(loglevel, "%s%s%s:%ld: invalid known_hosts entry",
+                    ctx->quiet ? __func__ : "", ctx->quiet ? ": " : "",
+                    l->path, l->linenum);
+        }
+        fprintf(ctx->out, "%s\n", l->line);
+        return 0;
+}
 
-        if ((r = sshkey_write(key, f)) != 0) {
-                error("%s: saving key in %s failed: %s",
-                    __func__, filename, ssh_err(r));
-        } else
-                success = 1;
-        fputc('\n', f);
-        fclose(f);
-        return success;
+int
+hostfile_replace_entries(const char *filename, const char *host,
+    struct sshkey **keys, size_t nkeys, int store_hash, int quiet)
+{
+        int r, fd, oerrno = 0;
+        int loglevel = quiet ? SYSLOG_LEVEL_DEBUG1 : SYSLOG_LEVEL_INFO;
+        struct host_delete_ctx ctx;
+        char *temp = NULL, *back = NULL;
+        mode_t omask;
+        size_t i;
+
+        memset(&ctx, 0, sizeof(ctx));
+        ctx.host = host;
+        ctx.quiet = quiet;
+        if ((ctx.skip_keys = calloc(nkeys, sizeof(*ctx.skip_keys))) == NULL)
+                return SSH_ERR_ALLOC_FAIL;
+        ctx.keys = keys;
+        ctx.nkeys = nkeys;
+
+        /*
+         * Prepare temporary file for in-place deletion.
+         */
+        if ((r = asprintf(&temp, "%s.XXXXXXXXXXX", filename)) < 0 ||
+            (r = asprintf(&back, "%s.old", filename)) < 0) {
+                r = SSH_ERR_ALLOC_FAIL;
+                goto fail;
+        }
+
+        omask = umask(077);
+        if ((fd = mkstemp(temp)) == -1) {
+                oerrno = errno;
+                error("%s: mkstemp: %s", __func__, strerror(oerrno));
+                r = SSH_ERR_SYSTEM_ERROR;
+                goto fail;
+        }
+        if ((ctx.out = fdopen(fd, "w")) == NULL) {
+                oerrno = errno;
+                close(fd);
+                error("%s: fdopen: %s", __func__, strerror(oerrno));
+                r = SSH_ERR_SYSTEM_ERROR;
+                goto fail;
+        }
+
+        /* Remove all entries for the specified host from the file */
+        if ((r = hostkeys_foreach(filename, host_delete, &ctx, host,
+            HKF_WANT_PARSE_KEY)) != 0) {
+                error("%s: hostkeys_foreach failed: %s", __func__, ssh_err(r));
+                goto fail;
+        }
+
+        /* Add the requested keys */
+        for (i = 0; i < nkeys; i++) {
+                if (ctx.skip_keys[i])
+                        continue;
+                do_log2(loglevel, "%s%sadd %s key to %s",
+                    quiet ? __func__ : "", quiet ? ": " : NULL,
+                    sshkey_type(keys[i]), filename);
+                if (!write_host_entry(ctx.out, host, keys[i], store_hash)) {
+                        r = SSH_ERR_INTERNAL_ERROR;
+                        goto fail;
+                }
+        }
+        fclose(ctx.out);
+        ctx.out = NULL;
+
+        /* Backup the original file and replace it with the temporary */
+        if (unlink(back) == -1 && errno != ENOENT) {
+                oerrno = errno;
+                error("%s: unlink %.100s: %s", __func__, back, strerror(errno));
+                r = SSH_ERR_SYSTEM_ERROR;
+                goto fail;
+        }
+        if (link(filename, back) == -1) {
+                oerrno = errno;
+                error("%s: link %.100s to %.100s: %s", __func__, filename, back,
+                    strerror(errno));
+                r = SSH_ERR_SYSTEM_ERROR;
+                goto fail;
+        }
+        if (rename(temp, filename) == -1) {
+                oerrno = errno;
+                error("%s: rename \"%s\" to \"%s\": %s", __func__,
+                    temp, filename, strerror(errno));
+                r = SSH_ERR_SYSTEM_ERROR;
+                goto fail;
+        }
+        /* success */
+        r = 0;
+ fail:
+        if (temp != NULL && r != 0)
+                unlink(temp);
+        free(temp);
+        free(back);
+        if (ctx.out != NULL)
+                fclose(ctx.out);
+        free(ctx.skip_keys);
+        if (r == SSH_ERR_SYSTEM_ERROR)
+                errno = oerrno;
+        return r;
 }
 
 static int